This present embodiments relate to identifying velocity scale. In medical diagnostic ultrasound imaging, the velocity scale is set to prevent aliasing.
Medical diagnostic ultrasound imaging systems perform autocorrelation between sets of received data to determine an average phase shift for flow or tissue velocity imaging. In Doppler processing, the phase shift represents the velocity of tissue or fluid. The velocity scale is selected to prevent aliasing. The velocity scale may be assigned as a preset for a given type of imaging or application. For example, different velocity scale presets may be provided for cardiac imaging than for imaging a thyroid.
The presets may be incorrect given the patient being imaged or other system settings. The user may adjust the velocity scale or other user input for changing the velocity scale. Based on expected image characteristics, the user adjust the scale to be sufficiently large to avoid aliasing but sufficiently small to maximize the dynamic range of velocities. However, user adjustment may be time consuming, difficult or undesired, resulting in longer scan times or sub-optimal image quality. When the imaging is changed, such as switching to imaging a different region of the patient, the previously selected velocity scale may be sub-optimal. The user may need to again manually adjust the velocity scale.
Automated anti-aliasing may be provided. U.S. Published Application No. 20040254467, the disclosure of which is incorporated by reference, discloses identification of the pulse repetition frequency by unwrapping phase information. Different possible velocities are determined from velocity estimates by applying different baseline shifts. The possible velocities with a minimal variance are selected as the unaliased velocities.